On Mon, Jan 30, 2012 at 02:02:14PM +0200, Avi Kivity wrote:
> On 01/30/2012 12:56 PM, Gleb Natapov wrote:
> > On Mon, Jan 30, 2012 at 12:24:11PM +0200, Avi Kivity wrote:
> > > > +
> > > > ctxt->ops->set_segment(ctxt, selector, &desc, base3, seg);
> > > > }
> > > >
> > > > @@ -2273,6 +2281,24 @@ static int load_state_from_tss32(struct
> > > > x86_emulate_ctxt *ctxt,
> > > > return emulate_gp(ctxt, 0);
> > > > ctxt->_eip = tss->eip;
> > > > ctxt->eflags = tss->eflags | 2;
> > > > +
> > > > + /*
> > > > + * If we're switching between Protected Mode and VM86, we need
> > > > to make
> > > > + * sure to update the mode before loading the segment
> > > > descriptors so
> > > > + * that the selectors are interpreted correctly.
> > > > + *
> > > > + * Need to get it to the vcpu struct immediately because it
> > > > influences
> > > > + * the CPL which is checked at least when loading the segment
> > > > + * descriptors and when pushing an error code to the new kernel
> > > > stack.
> > > > + */
> > > > + if (ctxt->eflags & X86_EFLAGS_VM)
> > > > + ctxt->mode = X86EMUL_MODE_VM86;
> > > > + else
> > > > + ctxt->mode = X86EMUL_MODE_PROT32;
> > > > +
> > >
> > > Shouldn't this be done after the set_segment_selector() block? My
> > > interpretation of the SDM is that if a fault happens while loading
> > > descriptors the fault happens with old segment cache, that is, it needs
> > > to be interpreted according to the old mode.
> > >
> > No, spec says:
> > Any errors associated with this loading and qualification occur in the
> > context of the new task.
>
> There aren't any possible errors until that point. But we don't want
> set_segment_selector() to use the new mode, it just changes the segment
> selectors, nothing else.
>
I agree with that set_segment_selector() part, but
load_segment_descriptor() happens on a new task.
--
Gleb.
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